It is known to etch patterns in process substrates using, for instance, plasmas. Typically a pattern is delineated on a process substrate surface by a photoresist procedure. It can be difficult, however, to monitor the depth to which a process substrate is etched in real time.
For instance, as described in a Patent to Branagh et al., U.S. Pat. No. 6,381,008, the etching of silicon dioxide can be accomplished in an etching chamber which contains fluorine or chlorine in the presence of a plasma. A reduced pressure, (eg. 10−5 Torr), ambient into which is introduced CF4, or more commonly, C2F6 or C4F8, gas is often utilized in industrial settings. While silicon dioxide is being etched in such a setting, certain etch products are formed, and if a beam of electromagnetic radiation is caused to pass through them, said products relatively strongly absorb energy at specific wavelengths, while energy present at other wavelengths is less strongly affected. Alternatively, energy provided by a present plasma serves to excite etch products and emissive electromagnetic radiation therefrom can be monitored. Careful monitoring of such intensity vs. wavelength spectra as a function of time can provide insight as to when silicon dioxide available for etching has been etched away, and when underlying silicon is reached. For instance, upon reaching silicon, the products of etching silicon dioxide are greatly reduced, (some small amount of said silicon dioxide etch products can still be produced as a result of typically undesirable over-etching laterally under photoresist defined boundaries, however). And it is possible that new products due to interaction of plasma and etching gas with silicon will appear and affect monitored intensity vs. wavelength spectra. This is particularly true where some oxygen is present and the underlying silicon is etched. However, the products of said interaction of plasma and etching gas with silicon, it is to be understood, typically demonstrate very different electromagnetic spectrum absorbence and/or emission characteristics. It is to be understood that the procedure comprising detection of products of an etch procedure as an indication of etch end point, can be practiced where other than silicon dioxide is etched, (eg. Al, SiN and W).
Said Patent to Branagh et al., U.S. Pat. No. 6,381,008 describes a method of identifying semiconductor etch end points comprising:
A. providing a semiconductor etch end-point detecting system comprising a spectrometer system which sequentially comprises, as encountered by entered electromagnetic radiation:                a. at least one means for receiving electromagnetic radiation;        b. a first reflecting means with a focal length less than two-hundred-fifty (250) millimeters;        c. at least one diffracting means;        d. a second reflecting means with a focal length less than two-hundred-fifty (250) millimeters; and        e. at least one detector means consisting of centrally located active detectors and laterally disposed packaging;said diffracting means being mounted on a stage which is positioned physically between said detector means on one side thereof, and said first and second reflecting means on a second side thereof; such that, in use, electromagnetic radiation is caused to enter said means for receiving electromagnetic radiation and reflect from said first reflecting means, then interact with said diffracting means such that a diffracted spectrum of electromagnetic radiation is caused to reflect from said second reflecting means and enter said detector, means, in which spectrometer system the first reflecting means has a focal length which is less than that of said second reflecting means and in which spectrometer system at least part of the detector means laterally disposed packaging is positioned behind said diffracting means in the sense that electromagnetic radiation reflecting from said second reflecting means is blocked direct access thereto by said diffracting means;said semiconductor etch end-point detecting system further including, in function combination with said spectrometer system, a means for effecting plasma etching of semiconductor comprising:        a. at least one vacuum chamber in which a semiconductor system to be etched is present during use;        b. at least one means for entering etching gas to said vacuum chamber;        c. at least one means for applying electrical energy to said etching gas;        d. at least one means for accessing electromagnetic radiation present in said vacuum chamber during a semiconductor etching process; and        e. at least one means for guiding said accessed electromagnetic radiation into said spectrometer system means for receiving a electromagnetic radiation;said method of identifying semiconductor etch end points further comprising chronologically repeatedly performing steps B. through F. in an evolving windowed factor analysis sequence until detecting semiconductor etch end point; said steps B. through F. being:        
B. during a semiconductor etch procedure in said vacuum chamber, obtaining a chronological sequence of electromagnetic radiation intensity vs. wavelength spectra from said spectrometer system detector means, said spectrometer system detector means being caused to access electromagnetic radiation present in said vacuum chamber during a semiconductor etching process;
C. selecting some number of electromagnetic radiation intensity vs. wavelength spectra from said chronological sequence of electromagnetic radiation intensity vs. wavelength spectra and forming them into a data matrix;
D. optionally selecting and deleting some set-off number of rows (columns) in said data matrix;
E. by applying mathematical matrix decomposition techniques to said data matrix determining value(s) of at least one representative parameter(s), each said representative parameter(s) being selected from the group consisting of: (members of a diagonal matrix and eigenvalues);
F. detecting semiconductor etch end point based upon change in said repeatedly calculated at least one representative parameter value(s) resulting from said chronologically repeated performance of steps B. through F.
A recent paper which describes the use of low pressure high density plasma etching of silicon dioxide is titled “Chemical Challenge of Submicron Oxide Etching”, by McNevin et al., J. Vac. Technol. B 15(2) (March/April 1997).
References cited in the Branagh et al. Patent are:
                U.S. Pat. No. 5,026,160 to Dorain et al.;        U.S. Pat. No. 5,991,023 to Morawski et al.;        U.S. Pat. No. 6,088,096 to Aoki et al.;        U.S. Pat. No. 6,181,418 to Palumbo et al.;and Articles cited therein are:        “An Integrated System of Optical Sensors For Plasma Monitoring And Plasma Control”, Anderson & Splichal, SPIE Vo. 2091, (1994). Real-time plasma etching utilizing sensors which measure plasma properties directly related to desired wafer features are discussed.        “Application of Chemometrics to Optical Emission Spectroscopy For Plasma Monitoring”, Splichal & Anderson, SPUE Vol. 1595, (1992) is also identified as monitoring of real-time plasma etching processes, based upon sensors which measure plasma properties that relate directly to desired etch features, is discussed.        “Sensor Systems For Real-time Feedback Control Of Reactive Ion Etching”, Benson et al. J. Vac. Sci. Technol. B 14(1), (January/February 1996), is identified as it describes use of an optical emission spectroscopy system sensor utilized in multivariant feedback control of plasma etching of wafers.        “Etching—.35 m Polysilicon Gates On A High-Density Helicon Etcher”, Kroft et al., J. Vac. Sci. Technol. B 14(1) (January/February 1996), is disclosed as it describes an example of application plasmas in selective polysilicon-to-oxide plasma etching procedures.        “In Situ Diode Laser Absorbtion Measurements Of Plasma Species In A Gaseous Electronics Conference Reference Cell Reactor”, Oh, Stanton, Anderson & Splichal, J. Vac. Sci. Technol B 13(3) (May/June 1995). is identified as it discusses monitoring of electromagnetic absorption during etching procedures.        “Optical Emission Spectroscopy of H2—CO and H2O—CH3OH Plasmas For Diamond Growth”, Manukonda & Dillon, J. Vac. Sci. Technol. A 13(3) (May/June 1995), is identified as it describes monitoring of electromagnetic emissions during a procedure in which diamond was grown.        “End Point Control Via Optical Emission Spectroscopy”, Litvak, J. Vac. Sci. Technol. B 14(1) (January/February 1996) describes the use of optical emission spectroscopy in identifying oxide etch end points, utilizing a conventional monochromator/photomultiplier system in conjunction with an end-point detecting algorithm.Many additional papers which describe plasma etching in the semiconductor fabrication area exist.        
Known papers which utilize Reflected Electromagnetic Radiation Intensity and Ellipsometry to investigate Etching of semiconductor systems are:                “Optical Etch-Rate Monitoring Using Active Device Areas: Lateral Interference Effects”, by Heimann, J. Electrochem. Soc., Vol. 132, No. 8, (1985), (note, this paper defines the terminology “lateral interference” as used herein);        “Ultraviolet-Visible Ellipsometry For Process Control During The Etching Of Submicron Features”, by Blayo et al., J. Op. Soc. Am., Vol. 12, No. 3, (1995);        “Multiwavelength Ellipsometry For Real-Time Process Control Of The Plasma Etching Of Patterned Samples”, Maynard et al., J. Vac. Sci. Technol. B 15(1) (1997);        “Thin Film Interferometry of Patterned Films”; Maynard et al., J. Vac. Sci., Technol. B, Vol. 13, (May/June 1995);        “Spectral Ellipsometry on Patterned Wafers”, Duncan, SPIE, Vol. 2637, (April 1995);        “Optical Analysis of Complex Multilayer Structures . . . ” Johs et al.; SPIE, Vol. 2253, (1994);        “Sample Depolarization Effects From Thin Films of ZnS . . . ”; Appl. Phys. Lett. 61(5), August (1994);        “Optical Etch Rate Monitoring: Computer Simulation Of Reflectance”, Heimann et al., J. Electrochem. Soc., Vol 131, No. 4, (1984).        
Known Patents are:                U.S. Pat. No. 5,929,993 to Johs, is disclosed as it describes application of Fourier Transforms in the determination of total film retardence in birefringent films.        
Patents identified in said 993 Patent are:                Patent to Krieger et al., U.S. Pat. No. 3,274,882;        Patent to Simila, U.S. Pat. No. 3,807,868;        Patent to. Gorman et al., U.S. Pat. No. 4,523,848;        Patent to Colombotto et al., U.S. Pat. No. 4,584,476;        Patent to Gawrisch et al., U.S. Pat. No. 4,909,630;        Patent to Johnson, U.S. Pat. No. 5,191,392.        Patent to Johs et al., U.S. Pat. No. 5,936,735 is disclosed as it describes an approach to analyzing data obtained by monitoring both coherent and incoherent addition of beam components which result from interaction with a patterned substrate.        
Patents identified in the 735 Patent are:                Patent to Woollam et al., U.S. Pat. No. 5,373,359;        Patent to Ducharme et al., U.S. Pat. No. 5,426,588;        Patent to Johs et al., U.S. Pat. No. 5,504,582; and        Patent to Green et al. U.S. Pat. No. 5,521,706.        
Another Patent, by Blayo et al. is U.S. Pat. No. 5,494,697.
A Search of Patents using key words “Substrate Etch” and “Fourier Transform provided:                U.S. Pat. No. 6,895,136 to Deliwala;        U.S. Pat. No. 6,891,685 to Deliwala et al.;        U.S. Pat. No. 6,869,881 to Deliwala;        U.S. Pat. No. 6,826,320 to Deliwala;        U.S. Pat. No. 6,823,112 to Deliwala;        U.S. Pat. No. 6,671,443 to Deliwala;        U.S. Pat. No. 6,633,076 to Krishnaraj et al.;        U.S. Pat. No. 6,611,636 to Deliwala;        U.S. Pat. No. 6,541,400 to Tian et al.;        U.S. Pat. No. 6,522,794 to Bischel et al.        U.S. Pat. No. 6,303,518 to Tian et al.;        U.S. Pat. No. 6,167,169 to Brinkman et al.;        U.S. Pat. No. 6,141,465 to Bischel et al.;        U.S. Pat. No. 6,118,908 to Bischel et al.;        U.S. Pat. No. 6,078,704 to Bischel et al.;        U.S. Pat. No. 5,978,524 to Bischel et al.;        U.S. Pat. No. 5,912,997 to Bischel et al.;        U.S. Pat. No. 5,911,018 to Bischel et al.;        U.S. Pat. No. 5,835,458 to Bischel Pet al.;        U.S. Pat. No. 5,724,463 to Deacon et al.;        U.S. Pat. No. 5,664,032 to Bischel et al.;        U.S. Pat. No. 5,647,036 to Deacon et al.;        U.S. Pat. No. 5,544,268 to Bischel et al.        
Also disclosed is a book titled “Numerical Recipes in C”, Cambridge Press, Press et al. Said book provides insight to application of Fourier and Lomb Transforms.
Need exists for improved, simple to practice methodology for accurately tracking the results of a process substrate etching procedure in real time.